feat: Add inner helpful classes in Expect

[asmirnov-backend]

Ref: #3461

Inner classes help to encapsulate the logic of using Expect and make it easier.

Before:

Expect.at(this, Attr.RHO)
    .that(phi -> new Dataized(phi).asNumber())
    .otherwise("must be a number")
    .it();

After:

new Expect.Number(Expect.at(this, Attr.RHO)).it();

Ref to comment

[yegor256]

@asmirnov-backend thanks! One comment above. Also, check this one: https://www.yegor256.com/2024/04/01/ping-me-please.html

[asmirnov-backend]

@yegor256 thanks for review! Comment resolved. Could you please rereview

[yegor256]

@asmirnov-backend thanks!